[hatari-devel] MFP timing

["Roger Burrows" <rfburrows@xxxxxxxxx>]

The TOS ACSI routines use 'tst.b $fffffa01' as part of a short-delay routine.  
I remember reading somewhere a long time ago that this was supposed to give a 1 
microsecond delay on all machines.

I'm implementing the equivalent delay in the EmuTOS ACSI routines (by a 
different method), so I thought I should verify my vague memory.  I did some 
timing tests on various machines, with accesses to $1000 (arbitrary) and to 
$fffffa01.  This is what I found (all times in microseconds and probably 
accurate to about 10%):
                     ST       Falcon      TT
tst.b $1000         1.6        0.36      0.17
tst.b $fffffa01     2.0        1.1       1.0

The timings for the first line are about what I would expect from the timing 
tables in the appropriate manuals.  The second line *almost* corresponds to my 
vague memory.

1. Can anyone here confirm (or refute) these findings?
2. I found a place in the Hatari code where extra wait states are added for 
access to the MFP.  It adds 4 cycles, which seems fine for the ST but not for 
the other machines.  Am I missing something?

Roger Burrows